1. Field
This patent specification relates to a method and apparatus for toner image fixing, and more particularly to a method and apparatus for toner image fixing using a sheet-shaped pressing member.
2. Description of Related Art
FIG. 1 shows a fixing apparatus for use in an image forming apparatus such as a copying machine, a facsimile machine, etc. The fixing apparatus of FIG. 1 includes a fixing roller 100, a pressure roller 101, a fixing heater 102, a thermo-sensor 103, a release pawl 104, a cleaning pad 105, a cleaning pad holder 106, a cleaning pad stopper 107, an entrance guide plate 108, and ejection rollers 109. The pressure roller 101 contacts under pressure with the fixing roller 100. The fixing heater 102 is arranged inside the fixing roller 100 to heat up the fixing roller 100. The thermo-sensor 103 detects a temperature of the fixing roller 100. The release pawl 104 releases a recording sheet from the fixing roller 100. The cleaning pad 105 cleans off the fixing roller 100. The cleaning pad holder 106 holds the cleaning pad 105. The cleaning pad stopper 107 is arranged downstream from the cleaning pad 105 in a rotation direction of the fixing roller 100. The entrance guide plate 108 is arranged at an entrance of the fixing apparatus from which a recording sheet is transported. The ejection rollers 109 are arranged at an exit of the fixing apparatus from which the recording sheet is ejected.
A recording sheet having a toner image is transported with the entrance guide plate 108 to a nip area formed between the fixing roller 100 and the pressure roller 101. The recording sheet is then subjected to heat and pressure in the nip area so that the toner image is melted and fixed on the recording sheet. After that, the recording sheet is ejected by the ejection rollers 109. The fixing roller 100 may allow toner particles to attach thereon time when the recording sheet passes through the nip area. However, the toner particles are cleaned off the fixing roller 100 with the cleaning pad 105.
A surface temperature of the fixing roller 100 is detected by the thermo-sensor 103. Based on the detected temperature, the fixing heater 102 is controlled to heat the fixing roller 100 by a controller (not shown).
Generally, such fixing apparatus commonly uses an infrared heater or a halogen heater as the fixing heater and includes a pair of fixing and pressure rollers. However, the pressure roller does not heat up quickly and can cause a failure of fixing. This is because the pressure roller has a relatively large heat capacity since it includes a metal core coated with a silicon rubber layer which is then covered by a releasing layer made of a Teflon tube, for example. In addition, a cost of such mechanism including the pressure roller is relatively high. Further, in this mechanism, the pressure roller needs to apply a relatively high pressure to the fixing roller in order to generate a nip area in a proper manner. This may stress and wrinkle the recording sheet.
The present application describes a novel fixing apparatus in use with an image forming apparatus. In one example, a novel fixing apparatus includes a fixing roller, a base, and a sheet-shaped pressing member. The fixing roller includes an inner heater. The base includes a mounting portion upstream from the fixing roller in a sheet transportation direction. The sheet-shaped pressing member includes a fixing side which is fixed to the mounting portion of the base and a free side downstream from the fixing side in the sheet transportation direction. The free side contacts the fixing roller with its upper surface under pressure to form a nip area. In this novel fixing apparatus, a recording sheet having a toner image thereon passes through the nip area formed between the fixing roller and the pressing member so as to be subjected to heat and pressure at the nip area.
The pressing member may have a property of a leaf spring.
The mounting portion of the base may be formed to have a plane surface so that a plane including the plane surface passes through a lower portion of the fixing roller.
The pressing member may have a length in the sheet transportation direction such that an edge of the free side is downstream from the nip area.
The above-described fixing apparatus may further include a stopper for stopping a vertical movement of the pressing member. This stopper is provided at a position of the base downstream from the nip area in the sheet transportation direction so as to contact the pressing member from its back side.
The stopper may be held for movement so as to adjust a vertical position of the pressing member.
A surface of the pressing member contacting the fixing roller may be formed in a cylindrical shape in part having a curvature equal to that of the fixing roller.
A plane of the pressing member upstream from the nip area may be slanted on a tangent line at an edge point of the nip area in the upstream side thereof in the sheet transportation direction.
A plane of the pressing member downstream from the nip area may be slanted on a tangent line, or a line away from the fixing roller, at an edge point of the nip area in the downstream side thereof in the sheet transportation direction.
The pressing member may be made of resin including fluoride resin or polyimide.
The pressing member may include a heat resistant plate member coated with a fluoride resin.
The heat resistant plate member may have a property for storing heat.
The pressing member may include a foam member or a anti-static member which may include carbon particles.
The pressing member may include a polymeric material including PFA and may contain an anti-static member including carbon particles in a weight ratio of from approximately 1.2% to approximately 6.4%.
The pressing member may include a metal member or a low electrical resistance.
The pressing member may be electrically isolated or have a resistance value of 1010 xcexa9cm or less.
The pressing member may include a surface including a plurality of projections and depressions, which surface contacts the fixing roller.
The plurality of projections and depressions may be slanted relative to the sheet transportation direction.
The pressing member may include a surface including a plurality of slits.
The pressing member may be configured to be thinner at the nip area than other portion thereof.
The pressing member may include a plurality of grooves formed in a main scanning direction in a back surface opposite to the nip area or a plurality of holes in a surface thereof downstream from the nip area in the sheet transportation direction.
The base may include a guide portion for guiding the recording sheet to the mounting portion and the fixing roller.
The guide portion may include a guide surface which forms a step relative to the plane of the mounting portion.
The free side of the pressing member may be subjected to a process for removing burrs.
The mounting portion may include edge portions different in length in the sheet transportation direction in accordance with a distribution of temperature such that an edge portion where the temperature is low is extended more than other edge portions where the temperature is high.
The base may be made of metal plates or be molded.
The base may be molded such that a holder for rotatably holding the fixing roller and the mounting portion are integrated with the base into a single piece unit.
The fixing roller, the pressing member, and the mounting portion may be arranged in a single unit so that the apparatus is detachable from an image forming apparatus after an installation.
The above-described fixing apparatus may further include an adjusting mechanism for adjusting a fixing position of the pressing member so as to change a region of the nip area in the surface of the pressing member.
The pressing member may be detachably fixed to the mounting portion of the base.
The pressing member may be fixed to the mounting portion with detachable fixing members at both ends, out of a sheet transportation passage, of the pressing member in a longitudinal direction.
The mounting portion may include holding portions for holding both edges of the pressing member.
The present application further describes a novel fixing apparatus. In one example, a novel fixing apparatus includes a plurality of rollers, a fixing belt, and a sheet-shaped pressing member. At least one of the plurality of rollers contains a heater. The fixing belt is extended under tension among the plurality of rollers and is cyclically moved by rotation of the plurality of rollers. The sheet-shaped pressing member includes a fixing side which is fixed and a free side downstream from the fixing side in a sheet transportation direction, the free side contacting the fixing belt with its upper surface under pressure to form a nip area. In this novel fixing apparatus, a recording sheet having a toner image thereon passes through the nip area formed between the fixing belt and the pressing member so as to be subjected to heat and pressure in the nip area.
The present application further describes a novel image forming apparatus. In one example, a novel image forming apparatus includes a fixing mechanism that fixes a toner image on a recording sheet. The fixing mechanism includes a plurality of rollers, a belt, and a pressing member. At least one of the plurality of rollers contains a heater. The belt is extended under tension among the plurality of rollers and is cyclically moved by rotation of the plurality of rollers. The pressing member presses the belt and is formed in a sheet shape. The pressing member includes a fixing side which is fixed and a free side downstream from the fixing side in a sheet transportation direction. The free side contacts the belt with its upper surface under pressure to form a nip area. In this image forming apparatus, a recording sheet having a toner image thereon passes through the nip area formed between the belt and the pressing member so as to be subjected to heat and pressure in the nip area.
The present application further describes a novel method of toner image fixing. In one example, a novel method includes the steps of providing, arranging, mounting, rotating, and transporting. The providing step provides a base including a mounting portion. The arranging step arranges a roller downstream from the plane mounting portion in a sheet transportation direction. The roller contains an inner heater for heating the roller. The mounting step mounts an elastic plate including a fixing side and a free side opposite to and downstream from the fixing side in the sheet transportation direction such that the fixing side is fixed to the mounting portion and the free side is brought in contact with the roller under pressure with an upper surface of the free side to form a nip area between the roller and the elastic plate. The rotating step rotates the roller. The transporting step transports a recording sheet having a toner image thereon into the nip area so as to be subjected to heat and pressure in the nip area.